Isoelectric Point Calculator
Calculate the isoelectric point (pI) of proteins from their amino acid sequence
Input Sequence
Ionizable Residues
Positive (basic)
Histidine (H)3
Lysine (K)4
Arginine (R)1
Total Basic8
Negative (acidic)
Aspartic acid (D)2
Glutamic acid (E)3
Cysteine (C)0
Tyrosine (Y)2
Total Acidic7
Isoelectric Point (pI)
7.90
Charge at Common pH Values
Charge at pH 7.0+0.27
Charge at pH 7.4 (physiological)+0.11
Sequence Length51 aa
Charge vs pH
pH 0pH 7pH 14
About Isoelectric Point
The isoelectric point (pI) is the pH at which a protein carries no net electrical charge. At this pH:
- The protein is least soluble
- The protein will not migrate in an electric field
- Positive and negative charges are balanced
This calculator uses the Henderson-Hasselbalch equation with pKa values for ionizable amino acid side chains.